Abstract : Spherical harmonic coefficients as usually derived from analysis of geomagnetic data on the spheroidal surface of the earth do not represent a true potential function. These coefficients differ significantly from those derived from a correct analysis of the same field extrapolated to a reference sphere, the largest difference being about 120 gamma in the g subscript 3 superscript o term. These differences are particularly important for subsequent extrapolation of the field either upward into the magnetosphere or downward toward the core. For instance, the position of a conjugate point as determined by a computer integration along a field line, can differ by more than 30 km. Using a simple computer program, some recent and older analyses have been modified to refer them to a sphere. Of several recent analyses suggested for consideration in selection of an international reference field, only one was originally referred to a true sphere. Since the sets are thus not consistent, the suggested selection of a simple median of these sets would not be desirable. The corrections required for the spheroidal shape of the earth and the implications of these corrections for the usage of the international reference field are factors to be considered in its selection. (Author)